Add dialBest to the API

[vasco-santos]

Type: Feature

Severity: N/A

Description:

There are use cases where we want to leverage libp2p to dial other peers using a specific protocol, but fallback to another one if that peer does not support the initial attempt. With the current API we need to do a cascade of dials, in order to do this, while libp2p could offer this in its API.

One example of this is in the Gossipsub implementation ChainSafe/gossipsub-js#34, where we intend to fallback to floodsubs if the peer does not support gossipsub.

We should have a utility to handle multi protocol negotiation, receiving a list of protocols and trying to dial by its order. An example could be:

const protocolPreferences = [gossipsubMulticodec, floodsubMulticodec]
libp2p.newStream(peerInfo, protocolPreferences, callback)
// or
libp2p.dialBest(peerInfo, protocolPreferences, callback)

This was discussed with @jacobheun in the Gossipsub PR

[dirkmc]

Sounds like a good improvement to me 👍

Should this just be an option on the dialProtocol() method? ie clients would specify either a string or an array as the second argument

[vasco-santos]

We could support an array of protocols, but in these type of APIs I usually prefer to be more specific. The naming would not suit greatly receiving an array.

Unless we add an option for fallbackProtocols

[wemeetagain]

dialProtocol accepts an array of protocols